Neem is a fast-growing tree that can reach a height of 15–20 metres (49–66 ft), and rarely 35–40 metres (115–131 ft). It is evergreen, but in severe drought it may shed most or nearly all of its leaves. The branches are wide and spreading. The fairly dense crown is roundish and may reach a diameter of 15–20 metres (49–66 ft) in old, free-standing specimens. The neem tree is very similar in appearance to its relative, the Chinaberry (Melia azedarach).

The opposite, pinnate leaves are 20–40 centimetres (7.9–15.7 in) long, with 20 to 31 medium to dark green leaflets about 3–8 centimetres (1.2–3.1 in) long. The terminal leaflet often is missing. The petioles are short.

The (white and fragrant) flowers are arranged in more-or-less drooping axillarypanicles which are up to 25 centimetres (9.8 in) long. The inflorescences, which branch up to the third degree, bear from 150 to 250 flowers. An individual flower is 5–6 millimetres (0.20–0.24 in) long and 8–11 millimetres (0.31–0.43 in) wide. Protandrous, bisexual flowers and male flowers exist on the same individual tree.

The fruit is a smooth (glabrous), olive-like drupe which varies in shape from elongate oval to nearly roundish, and when ripe is 1.4–2.8 centimetres (0.55–1.10 in) by 1.0–1.5 centimetres (0.39–0.59 in). The fruit skin (exocarp) is thin and the bitter-sweet pulp (mesocarp) is yellowish-white and very fibrous. The mesocarp is 0.3–0.5 centimetres (0.12–0.20 in) thick. The white, hard inner shell (endocarp) of the fruit encloses one, rarely two, or three, elongated seeds (kernels) having a brown seed coat.

The neem tree is noted for its drought resistance. Normally it thrives in areas with sub-arid to sub-humid conditions, with an annual rainfall of 400–1,200 millimetres (16–47 in). It can grow in regions with an annual rainfall below 400 mm, but in such cases it depends largely on ground water levels. Neem can grow in many different types of soil, but it thrives best on well drained deep and sandy soils. It is a typical tropical to subtropical tree and exists at annual mean temperatures of 21–32 °C (70–90 °F). It can tolerate high to very high temperatures and does not tolerate temperature below 4 °C (39 °F). Neem is one of a very few shade-giving trees that thrive in drought-prone areas e.g. the dry coastal, southern districts of India, and Pakistan. The trees are not at all delicate about water quality and thrive on the merest trickle of water, whatever the quality. In India and tropical countries where the Indian diaspora has reached, it is very common to see neem trees used for shade lining streets, around temples, schools and other such public buildings or in most people's back yards. In very dry areas the trees are planted on large tracts of land.

In April 2015, A. indica was declared a class B and C weed in the Northern Territory, Australia, meaning its growth and spread must be controlled and plants or propagules are not allowed to be brought into the NT. It is illegal to buy, sell, or transport the plants or seeds. Its declaration as a weed came in response to its invasion of waterways in the "Top End" of the territory.[8]

After being introduced into Australia, possibly in the 1940s, A. indica was originally planted in the Northern Territory to provide shade for cattle. Trial plantations were established between the 1960s and 1980s in Darwin, Queensland, and Western Australia, but the Australian neem industry did not prove viable. The tree has now spread into the savanna, particularly around waterways, and naturalised populations exist in several areas.[9]

The tender shoots and flowers of the neem tree are eaten as a vegetable in India. A souplike dish called Veppampoocharu (Tamil) (translated as "neem flower rasam") made of the flower of neem is prepared in Tamil Nadu. In West Bengal, young neem leaves are fried in oil with tiny pieces of eggplant (brinjal). The dish is called nim begun and is the first item during a Bengali meal that acts as an appetizer. It is eaten with rice.[11]

Neem is used in parts of mainland Southeast Asia, particularly in Cambodia aka sdov—ស្ដៅវ,[12] Laos (where it is called kadao), Thailand (where it is known as sadao or sdao), Myanmar (where it is known as tamar) and Vietnam (where it is known as sầu đâu and is used to cook the salad gỏi sầu đâu). Even lightly cooked, the flavour is quite bitter and the food is not enjoyed by all inhabitants of these nations, though it is believed to be good for one's health. Neem gum is a rich source of protein. In Myanmar, young neem leaves and flower buds are boiled with tamarind fruit to soften its bitterness and eaten as a vegetable. Pickled neem leaves are also eaten with tomato and fish paste sauce in Myanmar.

Insufficient research has been done to assess the purported benefits of neem, however.[16] In adults, short-term use of neem is safe, while long-term use may harm the kidneys or liver; in small children, neem oil is toxic and can lead to death.[16] Neem may also cause miscarriages, infertility, and low blood sugar.[16]

Neem is a key ingredient in non-pesticidal management (NPM), providing a natural alternative to synthetic pesticides. Neem seeds are ground into a powder that is soaked overnight in water and sprayed onto the crop. To be effective, it must be applied repeatedly, at least every ten days. Neem does not directly kill insects on the crop. It acts as an anti-feedant, repellent, and egg-laying deterrent, protecting the crop from damage. The insects starve and die within a few days. Neem also suppresses the hatching of pest insects from their eggs. Neem cake is often sold as a fertilizer.[18]

Neem oil has been shown to avert termite attack as an ecofriendly and economical agent.[19]

Applications of neem oil in the preparation of polymeric resins have been documented in the recent reports. The synthesis of various alkyd resins from neem oil is reported using a monoglyceride (MG) route and their utilization for the preparation of PU coatings.[20] The alkyds are prepared from reaction of conventional divalent acid materials like phthalic and maleic anhydrides with MG of neem oil. In other reports, different routes for preparation of polymeric resins from neem oil also are reported.[21]

The juice of this plant is a potent ingredent for a mixture of wall plaster, according to the Samarāṅgaṇa Sūtradhāra, which is a Sanskrit treatise dealing with Śilpaśāstra (Hindu science of art and construction).[22]

Toiletries: Neem oil is used for preparing cosmetics such as soap, shampoo, balms, and creams as well as toothpaste

Animal Treatment: Used to treat sweet itch and mud fever in horses

Toothbrush: Traditionally, slender neem twigs (called datun) are first chewed as a toothbrush and then split as a tongue cleaner.[23] This practice has been in use in India, Africa, and the Middle East for centuries. Many of India's 80% rural population still start their day with the chewing stick, while in urban areas neem toothpaste is preferred. Neem twigs are still collected and sold in markets for this use, and in rural India one often sees youngsters in the streets chewing on neem twigs. It has been found to be as effective as a toothbrush in reducing plaque and gingival inflammation.[24][25]

Neem gum is used as a bulking agent and for the preparation of special purpose foods.

Neem blossoms are used in Andhra Pradesh, Tamil Nadu, and Karnataka to prepare Ugadi pachhadi. A mixture of neem flowers and jaggery (or unrefined brown sugar) is prepared and offered to friends and relatives, symbolic of sweet and bitter events in the upcoming new year, Ugadi. "Bevina hoovina gojju" (a type of curry prepared with neem blossoms) is common in Karnataka throughout the year. Dried blossoms are used when fresh blossoms are not available. In Tamil Nadu, a rasam (veppam poo rasam) made with neem blossoms is a culinary specialty.

Cosmetics : Neem is perceived in India as a beauty aid. Powdered leaves are a major component of at least one widely used facial cream. Purified neem oil is also used in nail polish and other cosmetics.

Bird repellent: Neem leaf boiled in water can be used as a very cost-effective bird repellent, especially for sparrows.

Lubricant : Neem oil is non-drying and it resists degradation better than most vegetable oils. In rural India, it is commonly used to grease cart wheels.

Fertilizer : Neem has demonstrated considerable potential as a fertilizer. Neem cake is widely used to fertilize cash crops, particularly sugarcane and vegetables.

Plant protectant : Ploughed into the soil, it protects plant roots from nematodes and white ants, probably as it contains the residual limonoids.[citation needed] In Karnataka, people grow the tree mainly for its green leaves and twigs, which they puddle into flooded rice fields before the rice seedlings are transplanted.

Resin : An exudate can be tapped from the trunk by wounding the bark. This high protein material is not a substitute for polysaccharide gum, such as gum arabic. It may, however, have a potential as a food additive, and it is widely used in South Asia as "Neem glue".

Bark : Neem bark contains 14% tannin, an amount similar to that in conventional tannin-yielding trees (such as Acacia decurrens). Moreover, it yields a strong, coarse fibre commonly woven into ropes in the villages of India.

Soap : 80% of India's supply of neem oil now is used by neem oil soap manufacturers.[26] Although much of it goes to small-scale speciality soaps, often using cold-pressed oil, large-scale producers also use it, mainly because it is cheap. Additionally it is antibacterial and antifungal, soothing, and moisturising. It can be made with up to 40% neem oil.[26]]]. Generally, the crude oil is used to produce coarse laundry soaps.

Against pox viruses : In India, people who are affected with pox viruses are generally made to lie in bed made of neem leaves and branches.[citation needed] The belief is that it prevents the spreading of pox virus to others[citation needed] and has been in practice since early centuries.[citation needed]

Neem leaf or bark is considered an effective pitta pacifier because of its bitter taste. Hence, it is traditionally recommended during early summer in Ayurveda (that is, the month of Chaitra as per the Hindu Calendar which usually falls in the month of March – April).

During Gudi Padva, which is the New Year in the state of Maharashtra, the ancient practice of drinking a small quantity of neem juice or paste on that day, before starting festivities, is found. As in many Hindu festivals and their association with some food to avoid negative side-effects of the season or change of seasons, neem juice is associated with Gudi Padva to remind people to use it during that particular month or season to pacify summer pitta.

In Tamil Nadu during the summer months of April to June, the Mariamman temple festival is a thousand-year-old tradition. The Neem leaves and flowers are the most important part of the Mariamman festival. The statue of the goddess Mariamman will be garlanded with Neem leaves and flowers. During most occasions of celebrations and weddings the people of Tamil Nadu adorn their surroundings with the Neem leaves and flowers as a form of decoration and also to ward off evil spirits and infections.

In the eastern coastal state of Odisha the famous Jagannath temple deities are made up of Neem heart wood along with some other essential oils and powders.

Native of Chhattisgarh with Neem branches and leaves for Hareli Festival

In 1995, the European Patent Office (EPO) granted a patent on an anti-fungal product derived from neem to the United States Department of Agriculture and W. R. Grace and Company.[36] The Indian government challenged the patent when it was granted, claiming that the process for which the patent had been granted had been in use in India for more than 2,000 years. In 2000, the EPO ruled in India's favour, but W. R. Grace appealed, claiming that prior art about the product had never been published in a scientific journal. On 8March 2005, that appeal was lost and the EPO revoked the Neem patent.[36]

The biopesticide produced by extraction from the tree seeds contains limonoids. Currently, the extraction process has disadvantages such as contamination with fungi and heterogeneity in the content of limonoids due to genetic, climatic, and geographical variations.[37][38] To overcome these problems, production of limonoids from plant cell suspension and hairy root cultures in bioreactors has been studied,[39][40] including the development of a two-stage bioreactor process that enhances growth and production of limonoids with cell suspension cultures of A. indica.[41]